I have two 800A feeds ( 2 500kcmil/phase each feed)fed from two different breakers on the same substation. The 30 day maximum 15minute demand on these feeds is 250 on one and ~200 on the second. I am looking to change out the lugs on one of the breakers (to handle 4 500kcmil/phase) and feed these loads from one breaker to free up a breaker. Does this sort of load combining fall under 220.35? If it does from a calculation standpoint should both 30 day readings be multiplied by 1.25 and then added to verify total load per 220.35 (2)?
Combining Existing Feeder per 220.35
- Thread starter hopkins
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- Lockport, IL
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- Retired Electrical Engineer
Re: Combining Existing Feeder per 220.35
I don?t think you?re in ?calculation territory.? You are not creating or upgrading a service, so you need not be in 220. But 220 does provide a reasonable method of justifying your intended change from the load perspective, by showing that the existing load would be within the capacity of the one breaker and the two feeders. And for this method, yes you would add 25% to the 250 and the 200, get a result of 563, take note that this is less than 80% of 800, and call it good.
But I am confused over your intended final configuration. Both feeders come from the same substation, but where do they go? Are you serving two separate loads? Isn?t what you are doing essentially the same as double-lugging a 20 amp breaker in a residential panel, in order to serve two separate circuits? If so, although I can?t find any rules against it, and although the OCPD is adequate to protect the conductors, something about it seems odd to me. Anyone have any thoughts on this one?
I don?t think you?re in ?calculation territory.? You are not creating or upgrading a service, so you need not be in 220. But 220 does provide a reasonable method of justifying your intended change from the load perspective, by showing that the existing load would be within the capacity of the one breaker and the two feeders. And for this method, yes you would add 25% to the 250 and the 200, get a result of 563, take note that this is less than 80% of 800, and call it good.
But I am confused over your intended final configuration. Both feeders come from the same substation, but where do they go? Are you serving two separate loads? Isn?t what you are doing essentially the same as double-lugging a 20 amp breaker in a residential panel, in order to serve two separate circuits? If so, although I can?t find any rules against it, and although the OCPD is adequate to protect the conductors, something about it seems odd to me. Anyone have any thoughts on this one?
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